1. Field of the Invention
The present invention relates to a method for fabricating a liquid crystal display, and, more particularly, to a bonding machine for fabrication of a large size liquid crystal display (LCD), and a method for fabricating an LCD by using the same.
2. Discussion of the Related Art
Keeping pace with development of an information-oriented society, demands on displays increase gradually in a variety of forms and, recently, to meet the demands, different flat display panels, such as Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Electro Luminescent Display (ELD), Vacuum Fluorescent Display (VFD), and the like, have been under development, some of which are employed as displays in various apparatuses.
The LCDs have been most widely used the as mobile displays, while replacing the Cathode Ray Tube (CRT), owing to features and advantages of excellent picture quality, lightweight, thin size, and low power consumption. Besides the mobile-type LCDs of the notebook computer monitors, the LCDs are under development for televisions (TVs) for receiving and displaying broadcasting signals, and computer monitors.
Despite the various technical developments in the LCD, for serving as a display in different fields, the studies for enhancing the picture quality of the LCD as a display are inconsistent with the features and advantages of the LCD in many aspects. Therefore, for employing the LCD in various fields as a general display, the key to development of the LCD lies in whether the LCD can implement a high-quality picture such as high definition, high luminance, and a large sized screen, while having a lightweight, thin size, and a low power consumption.
The LCD may be fabricated by a generally known LCD injection method, in which one substrate having sealant patterned thereon to form an injection hole is bonded to the other substrate under a vacuum, and liquid crystal is injected therein through the injection hole, or by a liquid crystal dropping method, as disclosed in Japanese Patent Laid Open Publication Nos. 2000-284295, and 2001-005405, in which one substrate having liquid crystal dropped thereon and the other substrate are provided, and the two substrates, placed oppositely in a vertical direction, are brought closer to bond the two substrates.
Of the two methods, the liquid crystal dropping method is advantageous in that different components can be dispensed with the omission of many steps (such as the step of formation of the liquid crystal injection hole, the step of injection of liquid crystal, and the step of sealing the liquid crystal injection hole). Accordingly, studies have been recently made for development of various apparatuses for use in the liquid crystal dropping method.
FIGS. 1A and 1B illustrate related art bonding machines having the liquid crystal dropping method applied thereto. FIG. 2 illustrates a perspective view of key parts showing operation of substrate supporting means in a related art bonding machine, schematically.
The related art substrate assembler (bonding machine) is provided with a frame 10 forming an outer shape, stage parts 21 and 22, a sealant outlet part (not shown), a liquid crystal dropping part 30, chamber parts 31 and 32, chamber moving means, catch stop means, and stage moving means.
The stage parts have an upper stage 21 and a lower stage 22, and the upper stage 21 is provided with an electro-static chuck 28 for adsorbing the substrate by electrostatic adsorption. The sealant outlet part and the liquid crystal dropping part 30 are fitted to a side of a location at which the frame is bonded, and the chamber part has an upper chamber unit 31 and a lower chamber unit 32, detachable from each other, wherein the upper chamber unit 31 has a vacuum valve 23, and a hose 24 for evacuation of the chamber part connected thereto, and a gas purge valve 70 and a gas tube 71 for placing the chamber part into an atmospheric state.
The chamber moving means has a driving motor 40 for selective transfer of the lower chamber unit 32 to a location where the bonding is made, or to a location where discharge of the sealant and dropping of the liquid crystal is made. The stage moving means has a driving motor 50 for selective upward/downward movement of the upper stage 21.
The catch stop means supports the substrate 52 held at the upper stage 21 at diagonal positions of the substrate 52 during evacuation of the chamber, temporarily. The catch stop means is provided with rotating shafts 61, rotation actuators 63, elevation actuators 64, and supporting plates 62.
The steps of a process for fabricating an LCD by using a related art substrate assembler (bonding machine) will be explained in detail.
The upper stage 21 has one of the substrates (hereafter called as a “second substrate” 52) loaded thereon fixed thereto, and the lower stage 22 has the other one of the substrates (hereafter called as a “first substrate” 51) loaded thereon and fixed thereto.
Referring to FIG. 1A, in this state, the lower chamber unit 32 having the lower stage 22 is moved to a location for sealant coating and liquid crystal dropping by the chamber moving means 40.
Referring to FIG. 1B, when the sealant coating and the liquid crystal dropping are finished by the sealant outlet part and the liquid crystal dropping part 30, the lower chamber unit 32 is moved to a location for bonding the substrates by the chamber moving means 40. Then, the chamber units 31 and 32 are assembled by the chamber moving means 40, such that spaces the stages 21 and 22 are located therein are sealed, and the elevating actuators 64 and the rotating actuators 63 in the catch stop means are driven to bring the supporting plates 62 to two corners of the second substrate 52 held at the upper stage 31.
In this state, referring to FIG. 2, the adsorption force that holds the second substrate 52 is released, to drop the second substrate 52 onto the supporting plates 62 of the catch stop means.
Along with this, the chamber part is evacuated by using the vacuum valve 23 and the hose 34, and, when the chamber is evacuated, a voltage is applied to the electro-static chuck 28 to hold the second substrate 52 by electrostatic adsorption, and the rotation actuator 63 and the elevation actuator 64 of the catch stop means are driven, so that the supporting plate 62 and the rotating shafts 61 do not interfere in bonding the two substrates together.
Then, in this vacuum state, as the upper stage 21 is moved downward by the state moving means 50, the second substrate 52 held at the upper stage 21 is bonded to the first substrate 51 held at the lower stage 22.
Upon completion of the bonding of the two substrates by means of the upper and lower stages 21 and 22, the gas purge valve 80 is opened, to return the chamber part into an atmospheric state.
Then, finished substrates are unloaded, and carried to a subsequent process, and, at the same time, new substrates are carried in, to continuously carry out substrate bonding.
However, the related art method for fabricating LCD having the liquid crystal dropping method applied thereto has the following problems.
First, when the chamber part is at a vacuum, because, though the upper stage adsorbs the second substrate by means of the electro-static chuck, the lower stage does not adsorb the first substrate, the first substrate on the lower stage is likely to be involved in position change in evacuation of the chamber part, which leads to misalignment of the two substrates to be bonded.
Second, the bonded substrate are likely to be involved in distortion, which leads to a defective bonding of the substrates, due to sudden pressure change during releasing the vacuum of the chamber part upon completion of the substrate bonding. This is because there has been no system for fixing the bonded substrates since the chamber part is placed in an atmospheric state after the upper stage is moved upward upon finishing the substrate bonding.
Of course, by generating the electro-static force at the lower stage to hold bottom of the bonded substrates, there is still a problem of distortion of the first substrate with respect to the second substrate in an upper part of the bonded substrates because the lower stage only holds the first substrate in a lower part of the bonded substrates.
Third, a plurality of fingers in the related art robot arm of the carrying device for carrying out loading of the substrate smoothly droop as the fingers have a small width compared to a length. Particularly, the substantially greater droop of fore ends of the fingers (i.e., opposite parts of a part connected to the carrying device) leads the substrate to droop also, which causes damage to different parts of the substrate.
Fourth, the unloading of substrates from the chamber part after loading of substrates to be bonded into the chamber part by means of the lower chamber unit 22 limits the reduction of a substrate loading/unloading time period.